Electrophotography is a widely used method of information processing. Xerography is a form of electrophotography that is used to make copies of documents. Xerographic copiers are extensively used in a variety of environments, such as offices, libraries, and educational institutions.
The basic elements of a xerographic copier are well known to those skilled in the art. A light source is used to form an electrostatic image of an original document on a photosensitive medium. The photosensitive medium, as it is carried through the copier, travels adjacent to a source of tiny plastic particles. The plastic particles are called toner. The electrostatic force of the image on the photosensitive medium attracts the toner to the surface of the photosensitive medium. This provides a developed image of toner particles on the surface of the photosensitive medium. The toner image is transferred through electrostatic charges to an image receptor, which is normally a sheet of paper or plastic. The image receptor passes through a heating device which melts the toner particles thereby fixing the image of the original onto the image receptor.
A supply of the toner used to create the final image is stored in a toner module. Also within the toner module is a supply of ferromagnetic carrier particles. The toner particles are electrostatically attracted to the ferromagnetic carrier particles. The combination of toner and ferromagnetic carrier particles is called the developer. Conventionally, a developer roller, comprising a sleeve rotating around a plurality of magnetic pole pieces, carries developer from the interior of the toner module to a point at which it contacts the photosensitive medium. After the electrostatic image pulls the toner away from the ferromagnetic carrier particles, the magnetic forces within the toner module transport the ferromagnetic carrier particles back to a position where they are remixed with toner.
As it is well known in the art, the ferromagnetic carrier particles lose their electrostatic attractiveness through use. As time passes, some of the toner particles become imbedded in the carrier particles. As a result, the embedded toner particles shield the electrostatic force of the carrier particles and additional toner particles will not adhere to the surface of the particles. Thus, the ferromagnetic carrier particles in the developer must be replaced periodically. As the toner particles are depleted through use, the toner in the developer must also be replaced.
With conventional toner modules, the replacement of used developer is a messy, time consuming, and costly process. To remove developer from a conventional toner module, the toner module must be opened. Blades or brushes are commonly used to scrape the developer off the magnetic surfaces within the toner module. The developer is either vacuumed or shaken out as it is being scraped. To add new developer, the developer is poured from a container directly into the toner module.
Since the developer is composed of tiny plastic and iron particles, it has the consistency of a powder. Like a powder, the slightest movement of air sends developer flying. When the developer is scraped and vacuumed or shaken from the toner module, it is inevitable that some of the developer becomes airborne and eventually settles in undesirable areas. Some of the developer settles inside the copier itself or on other equipment where the particles can cause abrasive damage. Developer can also end up on clothes or carpet where it is difficult to remove. Like developer removal, the process of adding new developer by pouring it into the toner module also has a tendency to produce airborne particles which settle in undesirable places.
In a color xerographic copier, several toner modules, each with a different color of toner, are used. The developer must periodically be replaced in each one of the toner modules. Thus, the problems mentioned above are multiplied and there is an additional problem of color contamination. Color contamination results when developer particles intended for one toner module become airborne and end up in another toner module containing a different toner color.
More recently, laser printers have become popular office machines. As is known to those skilled in the art, laser printers tend to be constructed with print engines which are substantially identical to those used in xerographic copiers. A raster-scanned laser beam is used to create the developed image directly on the photosensitive medium in a laser printer. After the image is created on the photosensitive medium, the printer process is identical to that in a xerographic copier, i.e. toner particles, which have been stored in toner modules, are deposited onto the photosensitive medium. Even more recently, color laser printers have become popular.
Therefore, there is a need for a toner module for an electrophotographic print engine or laser print engine which provides for a simpler, cleaner method of replacing developer.